Mammalian cells have cytoskeletal networks that are associated with their plasma membrane. The cytoskeleton is comprised of a dense network of actin filaments and associated actin-binding proteins. Components of both the cytoskeletal network and the plasma membrane are important for cellular signalling by, for example, localizing and focusing critical signalling molecules.
Certain mammalian cells comprise multichain surface receptors that enable a cell to respond to changes in the environment outside of the cell. One such multichain receptor is a T cell receptor (TCR) located on the surface of T lymphocytes. A TCR is a multichain, heteromeric structure composed of an antigen binding domain comprising .alpha. and .beta. chains, and non-covalently associated signal transducing complexes, including CD3-.gamma., .delta. and .epsilon. chains, and the .zeta. chains. Signal transduction events produced by TCR ligation with major histocompatibility complexes (MHC) induce a variety of cytoplasmic metabolic changes. For example, gene transcription and production of interleukin-2 (IL-2) are promoted by TCR ligation with MHC molecules.
Abnormalities in T lymphocyte function can arise through deregulation of signalling in T cells. Such diseases include, for example, autoimmune diseases, immunodeficiency diseases and immunoproliferative diseases. T lymphocyte function also contributes to graft rejection. To develop compounds that regulate the activity of molecules involved in T cell function, there must be an understanding of the molecules and interactions involved in such T cell related diseases.
Prior investigators have suggested that ligand binding converts surface immunoglobulin (Ig) to a detergent insoluble form, and that Ig receptors subsequently undergo extensive degradation accompanied by the appearance of a detergent soluble membrane product (Braun et al., J. Immunol. 128:1198-1204, 1982). Parsey et al. (J. Immunol. 151:1881-1893, 1993) hypothesize about a connection between actin polymerization and the ability of immobilized anti-CD3 antibodies to stimulate changes in cell shape and F-actin morphology. Furthermore, the expression of four src-family genes associated with T cell activation was shown to be specifically blocked by cyclosporine (Furue et al., J. Immunol. 144(2):736-739, 1990). Prior investigators, however, have failed to teach or appreciate that actin polymerization in T lymphocytes is specifically regulated by the presence of a particular motif (i.e., an immunoreceptor tyrosine-based activation motif; ITAM) of a .zeta. chain or .epsilon. chain of a TCR.
Although therapeutics exist that regulate immune activity in an animal, problems have arisen due to the non-specific nature and harmful side effects of such drugs. Despite a long-felt need to discover compounds that specifically regulate T cell activity with minimal side-effects, the complexity and lack of understanding of signal transduction networks in a T cell has hindered the development of such compounds. The present invention offers a method and product that permits regulation of specific steps of a signal transduction pathway in cells having ITAM-containing receptors.